A mass spectrometer system comprises a chamber having an ion emitting unit to emit metal ions in the chamber with a communicating hole; a neutral molecule introduction unit; another gas introduction unit; a controller controlling a temperature of a region where metal ions attach to the neutral molecules; and a mass analyzer for the neutral molecules with the metal ions, wherein plotting an attachment energy of the metal ions attached to the neutral molecules in the chamber along an abscissa and the temperature of the region where the metal ions attach to the neutral molecules along an ordinate, the controller adjusts the temperature of the region so as to fall within a range obtained by excluding a range corresponding to the temperature of the region from 150 to 200° C. from a range surrounded by the temperatures of the region [° C.]=150×attachment energy [eV], 100×attachment energy [eV]−50, and 20° C., and attachment energies [eV]=2.1 and 0.5.